During the Second World War, Britain's Royal Air Force was divided into a number of functional and geographic commands in line with an organisation that had first been implemented in 1936. Bomber Command was based in Great Britain and was responsible for bombing targets in enemy-controlled Europe. At the height of its operations in late 1944 Bomber Command comprised over 80 operational squadrons. These squadrons were organised into several groups on the basis of their role, the type of aircraft they operated, and the locations of the airfields from which they operated. In 1939 these groups were numbered 2-5 and by the end of the war Bomber Command comprised 1, 2, 3, 4, 5, 6 (Canadian), 8 (Pathfinder), 100 (Special Duties), and 91, 92 and 93 (Training) groups. Approximately 10,000 Royal Australian Air Force personnel served with Bomber Command and 3,486 were killed.